Almost every modern power management integrated circuit (IC) incorporates a variety of different LDOs to provide stable and accurately regulated voltage supplies. The LDO drops the input voltage Vin by the pass device to the output voltage Vout to provide a regulated supply that is free of any noise. With steadily increasing demand for more regulated voltage supplies (e.g., a modern power management IC (PMIC) can include more than 20 LDOs), the current consumption (Iq) of the LDOs becomes the key parameter for power efficiency.
A class of LDOs may be very efficient in normal operation mode where the output voltage Vout is well below the input voltage Vin, the quiescent current Iq at low load condition is well controlled to a low value (e.g., <20 μA), and the current efficiency is very good. However, in a scenario where the input voltage Vin of the LDO is close to the desired regulated output voltage, i.e., in the so-called dropout operation region, the quiescent current Iq of the LDO increases (e.g., up to several mA) and is independent of the load current. This behavior heavily disrupts the power efficiency of the LDO.